Re: Objects and Relations
From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Wed, 31 Jan 2007 09:33:50 +0100
Message-ID: <45c0546e$0$333$e4fe514c_at_news.xs4all.nl>
>
> Yeah; the transactional semantics strike me as more
> or less independent from the logical model. However
> I should note that I remain distinctly undereducated
> in relational implementation, so I may just be kidding myself.
> Especially note that Jan Hidders expressed skepticism of the idea.
>
> As to a list algebra itself, it turned out not to be necessary;
> everything I wanted to do with a list algebra I could do with
> the relational algebra. However we do have to add some
> modest semantics to a few primitives. For example,
> if we are doing a "group by" with a fold of a function
> that isn't both commutative and associative, we have to
> specify the order of the aggregation or else our result
> is nondeterministic. Thus I imagine a few small additional
> semantics, such as that folds ("aggregation" in relational
> terminology) of non-commutative-and-associative functions
> must be performed on lists and not unordered relations,
> and they are specified to be performed in list order, and
> that joins with operands that aren't side-effect-free have
> the same semantics. Actually that's about all you need.
> Oh, and some imperative operators: insert-at and
> delete-at, for positional inserts and deletes that
> "renumber" the list after the fact. These can be
> defined in terms of relations though.
Date: Wed, 31 Jan 2007 09:33:50 +0100
Message-ID: <45c0546e$0$333$e4fe514c_at_news.xs4all.nl>
Marshall wrote:
> mAsterdam wrote:
>> Marshall wrote: >> >>> Yes. I note that often when these kinds of comparisons are made, >>> they are implicitly made between a non-thread-safe, non-transactional >>> array, and a rowstore with full transactional semantics. >> I remember you said you were working on a list algebra. >> Are/were you aiming to construct it in such a way >> that full transactional semantics would be a breeze?
>
> Yeah; the transactional semantics strike me as more
> or less independent from the logical model. However
> I should note that I remain distinctly undereducated
> in relational implementation, so I may just be kidding myself.
> Especially note that Jan Hidders expressed skepticism of the idea.
>
> As to a list algebra itself, it turned out not to be necessary;
> everything I wanted to do with a list algebra I could do with
> the relational algebra. However we do have to add some
> modest semantics to a few primitives. For example,
> if we are doing a "group by" with a fold of a function
> that isn't both commutative and associative, we have to
> specify the order of the aggregation or else our result
> is nondeterministic. Thus I imagine a few small additional
> semantics, such as that folds ("aggregation" in relational
> terminology) of non-commutative-and-associative functions
> must be performed on lists and not unordered relations,
> and they are specified to be performed in list order, and
> that joins with operands that aren't side-effect-free have
> the same semantics. Actually that's about all you need.
> Oh, and some imperative operators: insert-at and
> delete-at, for positional inserts and deletes that
> "renumber" the list after the fact. These can be
> defined in terms of relations though.
Thanks.
'at' - sounds/is navigational or what? :-)
Pity I don't have the time to get into this right now. If I remember correctly last time we got to this, concurrency issues arose.
I'll be back in a few days. Received on Wed Jan 31 2007 - 09:33:50 CET